In hydraulic or airless paint spraying, a pump is utilized to pressurize the paint to pressures of 2,000 pounds per square inch and greater so that the paint can be atomized upon release from a nozzle in a spray gun. The type of pump preferably used for this purpose is the double acting piston pump because of the piston pump's ability to handle high viscosity paints or coatings easily and the capability of the double acting pump to pump fluid on both the upstroke and downstroke of the piston thereby providing a relatively even flow of paint to the nozzle of the spray gun. In the double acting piston pump a stepped piston reciprocates in a cylinder having an inlet at one end and an outlet at the second end whereby two chambers are formed in the cylinder by the stepped piston. The first or inlet chamber is defined by the piston head and the cylinder and the outlet or exhaust chamber is formed at the opposite end of the piston and is defined by the stepped down portion of the piston and the cylinder wall. A transfer or bypass valve is disposed in the piston to transfer paint from the inlet chamber to the outlet chamber. On the intake stroke of the piston the transfer valve is closed while simultaneously the inlet valve is opened by vacuum so as to draw paint into the inlet chamber. On the down or exhaust stroke of the piston, the inlet valve is closed by the fluid pressure exerted on it while the bypass valve is opened by the fluid pressure exerted on it so as to permit the paint in the inlet chamber to pass through the transfer valve and into the exhaust chamber. Because of the volume difference between the inlet and exhaust chambers, approximately half the paint transferred to the exhaust chamber is forced through the pump outlet during this stroke while the other half remains in the exhaust chamber. On the next intake stroke, as the piston withdraws in the cylinder it forces the remaining paint in the exhaust chamber through the pump outlet while at the same time paint is brought in through the inlet valve into the inlet chamber. An upper seal packing located at the upper extremity of the cylinder sealingly engages around the stepped down portion of the piston and seals the outlet chamber of the cylinder from the exterior. A lower seal packing located within the cylinder sealingly engages around the piston head and separates the outlet and inlet chambers.
Such hydraulic or airless high pressure paint pumps are used extensively in the painting industry for the painting of new constructions, industrial installations, etc. For the most part the only maintenance required for such pumps is the replacement of parts or components which are subject to wear. Such replacement of worn parts requires a rebuilding or refurbishing of the pump and generally involves the replacement of the packings or seals in the pumps which eventually leak as a result of wear and the replacement of the inlet and bypass valves which are also subject to wear and leakage. In order to accomplish this pump rebuilding or refurbishing, it is necessary to dismantle the pump section which includes removal of the pump piston so as to gain access to the seal packings and the inlet and bypass valves. The high pressure or airless paint sprayers or pumps currently available in the market are adapted to have their pump or fluid sections disengaged and removed from the driving components of the pump system so as to permit the dismantling thereof. However, because of the relatively complex nature of pump construction and arrangement of the parts therein, rebuilding of the pump and reassembly of the parts thereof requires special care and close attention and sometimes the use of special tools in order to insure a correct and proper rebuilding and reassembly, otherwise, damage or leakage in operation may result. Specifically, the packing seals used in such pumps generally consist of a plurality of sealing elements which may be formed into a unit wherein the sealing elements or sealing lips of the seal are oriented in one direction for effective sealing. The pump's upper packing has its sealing lips oriented downwardly while the lower packing has its sealing lips oriented or directed upwardly. If these seals are incorrectly oriented during assembly of the pump, improper sealing will result and leakage will occur. It is also critical during reassembly of the pump that the piston rod be properly centered and aligned for insertion into the pump cylinder otherwise again the seals may be damaged causing the pump to leak during operation. This piston insertion step is further exacerbated because a significant amount of force is required in order to overcome the resistance exerted by the seals during insertion of the piston rod into the cylinder so that the use of a hammer or mallet is frequently necessary to drive the piston rod into place. Thus, included with pump rebuilding kits provided by manufacturers are detailed instructions on the proper installation of the packing seals and assembly of the piston and cylinder and some manufacturers also include a guide tool to insure the proper alignment of the piston and cylinder during assembly. However, pumps rebuilt by painting contractors or their employees frequently leak in operation or are otherwise damaged because of the difficulty of such rebuilding or the inability or failure to follow rebuilding instructions carefully. An alternative available to painting contractors is to have the pumps rebuilt by the manufacturers thereof. The obvious drawbacks to this are the extended period of time that the pump is unavailable to the contractor and the expense therefor.
Another problem relating to the rebuilding of such pumps concerns the replacement of worn valves particularly the lower inlet valve. This valve is located in the well of the inlet valve housing at the pump inlet and the elements consist of a valve seat, a ball or flat valve, and a valve cage for limiting and guiding the movement of the ball or flat valve. A retainer is employed for retaining the valve elements in the valve housing. In rebuilding this portion of the pump the retainer must first be removed from the valve housing in order to gain access to the valve elements; next the valve cage is removed, then the ball or flat valve is removed and finally the valve seat is removed. However, after a period of use in pumping paint, a residual of paint accumulates in and around the valve elements and particularly the valve cage and after drying makes it difficult to remove the valve cage from the well of the housing. In such a case it is often necessary to utilize a tool, such as a screwdriver or pick, to pry the valve cage loose from the valve housing well so as to free the remaining valve elements for removal.